Timer in Java with GUI

Question

I have created a timer with GUI in Java.

Here's the code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.Toolkit;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import javax.swing.text.NumberFormatter;

import static javax.swing.WindowConstants.EXIT_ON_CLOSE;

public class Counter {
   private JButton button;
   private JFormattedTextField hours;
   private JFormattedTextField minutes;
   private JFormattedTextField seconds;

   private Timer timer;
   private int delay = 1000;
   private ActionListener taskPerformer = new ActionListener() {
       public void actionPerformed(ActionEvent evt) {

                   if(sec >= 1) {
                       sec = sec - 1;
                       seconds.setText(String.valueOf(sec));
                   }
                   else if(sec == 0 && min > 0) {
                       sec = 59;
                       min = min - 1;
                       seconds.setText(String.valueOf(sec));
                       minutes.setText(String.valueOf(min));
                   }
                   else if(min == 0 && hrs > 0) {
                       sec = 59;
                       min = 59;
                       hrs = hrs - 1;
                       seconds.setText(String.valueOf(sec));
                       minutes.setText(String.valueOf(min));
                       hours.setText(String.valueOf(hrs));
                   }
                   if(hrs == 0 && min == 0 && sec == 0) {
                       Toolkit.getDefaultToolkit().beep();
                       JOptionPane.showMessageDialog(null,"Countdown ended!","Ende", JOptionPane.CANCEL_OPTION);
                       timer.stop();
                   }
       }
   };

   private int hrs;
   private int min;
   private int sec;

   public static void main(String[] args) throws InterruptedException {

       SwingUtilities.invokeLater(Counter::new);
   }

   Counter() {
       JFrame frame = new JFrame();
       frame.setSize(300, 200);
       frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
       JPanel panel = new JPanel(new BorderLayout());
       JPanel subpanel1 = new JPanel(new GridLayout(2, 3));

       /* 
        * The following lines ensure that the user can 
        * only enter numbers.
       */

       NumberFormat format = NumberFormat.getInstance();
       NumberFormatter formatter = new NumberFormatter(format);
       formatter.setValueClass(Integer.class);
       formatter.setMinimum(0);
       formatter.setMaximum(Integer.MAX_VALUE);
       formatter.setAllowsInvalid(false);
       formatter.setCommitsOnValidEdit(true);

       //"labeling"

       JTextField text1 = new JTextField();
       text1.setText("hours:");
       text1.setEditable(false);

       JTextField text2 = new JTextField();
       text2.setText("minutes:");
       text2.setEditable(false);


       JTextField text3 = new JTextField();
       text3.setText("seconds:");
       text3.setEditable(false);

       //fields for minutes and seconds
       hours = new JFormattedTextField(formatter);
       minutes = new JFormattedTextField(formatter);
       seconds = new JFormattedTextField(formatter);
       hours.setText("0");
       minutes.setText("0");
       seconds.setText("0");

       JPanel subpanel2 = new JPanel();

       /*
        * When the user presses the OK-button, the program will
        * start to count down.
       */

       button = new JButton("OK");
       button.addActionListener(new ActionListener() {
           @Override
           public void actionPerformed(ActionEvent actionEvent) {
               hrs = Integer.valueOf(hours.getText());
               min = Integer.valueOf(minutes.getText());
               sec = Integer.valueOf(seconds.getText());
               button.setEnabled(false);

               //Timer for one second delay
               Timer timer = new Timer(delay, taskPerformer);
               timer.start();  


           }
       });

       //Reset-button
       JButton button2 = new JButton("Reset");
       button2.addActionListener(new ActionListener() {
           @Override
           public void actionPerformed(ActionEvent actionEvent) {
               hours.setText("0");
               minutes.setText("0");
               seconds.setText("0");
               button.setEnabled(true);
               hrs = 0;
               min = 0;
               sec = 0;
           }
       });

       subpanel1.add(text1);
       subpanel1.add(text2);
       subpanel1.add(text3);
       subpanel1.add(hours);
       subpanel1.add(minutes);
       subpanel1.add(seconds);
       subpanel2.add(button);
       subpanel2.add(button2);
       panel.add(subpanel1, BorderLayout.CENTER);
       panel.add(subpanel2, BorderLayout.PAGE_END);
       frame.add(panel);
       frame.setVisible(true);
   }
}

I would appreciate any suggestions on improving the code!

Answer 1

A few things I noticed:

Quite a few of your variables can be marked final. From my understanding pretty much any variable where the underlying object doesn't get reassigned to a new object.

Instead of 3 separate variable for the time parts, you could use java.time.LocalTime to hold the time parts. Not only does this reduce your code, but it simplifies the count down portion in that subtracting 1 second will adjust the other fields automatically.

Since Integer.valueOf uses Integer.parseInt anyway, I think it would be better, in this case, to use Integer.parseInt

You misspelled the title of the message dialog when the countdown is done.

I think INFORMATION_MESSAGE is a better icon, for the message dialog, than CANCEL_OPTION, in this case.

The throws clause in the main declaration is redundant.

With these adjustments your code could look like this:

import javax.swing.*;
import javax.swing.text.NumberFormatter;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import java.time.LocalTime;

import static javax.swing.WindowConstants.EXIT_ON_CLOSE;

public class Counter {
    private final JButton button;
    private final JFormattedTextField hours;
    private final JFormattedTextField minutes;
    private final JFormattedTextField seconds;

    private final Timer timer;
    private final int delay = 1000;
    private final ActionListener taskPerformer = new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
            time = time.minusSeconds(1);
            if (time.equals(LocalTime.MIN)) {
                Toolkit.getDefaultToolkit().beep();
                JOptionPane.showMessageDialog(null, "Countdown ended!", "Ended", JOptionPane.INFORMATION_MESSAGE);
                timer.stop(); 
            }
            seconds.setText(String.valueOf(time.getSecond()));
            minutes.setText(String.valueOf(time.getMinute()));
            hours.setText(String.valueOf(time.getHour()));
        }
    };

    private LocalTime time = LocalTime.of(0, 0, 0);

    public static void main(String[] args) {

        SwingUtilities.invokeLater(Counter::new);
    }

    Counter() {
        timer = new Timer(delay,taskPerformer);
        JFrame frame = new JFrame();
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new BorderLayout());
        JPanel subPanel1 = new JPanel(new GridLayout(2, 3));

        /*
         * The following lines ensure that the user can
         * only enter numbers.
         */

        NumberFormat format = NumberFormat.getInstance();
        NumberFormatter formatter = new NumberFormatter(format);
        formatter.setValueClass(Integer.class);
        formatter.setMinimum(0);
        formatter.setMaximum(Integer.MAX_VALUE);
        formatter.setAllowsInvalid(false);
        formatter.setCommitsOnValidEdit(true);

        //"labeling"

        JTextField text1 = new JTextField();
        text1.setText("hours:");
        text1.setEditable(false);

        JTextField text2 = new JTextField();
        text2.setText("minutes:");
        text2.setEditable(false);


        JTextField text3 = new JTextField();
        text3.setText("seconds:");
        text3.setEditable(false);

        //fields for minutes and seconds
        hours = new JFormattedTextField(formatter);
        minutes = new JFormattedTextField(formatter);
        seconds = new JFormattedTextField(formatter);
        hours.setText("0");
        minutes.setText("0");
        seconds.setText("0");

        JPanel subPanel2 = new JPanel();

        /*
         * When the user presses the OK-button, the program will
         * start to count down.
         */

        button = new JButton("OK");
        button.addActionListener(actionEvent -> {
            time = LocalTime.of(Integer.parseInt(hours.getText()), Integer.parseInt(minutes.getText()), Integer.parseInt(seconds.getText()));
            button.setEnabled(false);
            //Timer for one second delay
            timer.start();
        });

        //Reset-button
        JButton button2 = new JButton("Reset");
        button2.addActionListener(actionEvent -> {
            hours.setText("0");
            minutes.setText("0");
            seconds.setText("0");
            button.setEnabled(true);
            time = LocalTime.of(0, 0, 0);
            timer.stop();
        });

        subPanel1.add(text1);
        subPanel1.add(text2);
        subPanel1.add(text3);
        subPanel1.add(hours);
        subPanel1.add(minutes);
        subPanel1.add(seconds);
        subPanel2.add(button);
        subPanel2.add(button2);
        panel.add(subPanel1, BorderLayout.CENTER);
        panel.add(subPanel2, BorderLayout.PAGE_END);
        frame.add(panel);
        frame.setVisible(true);
    }
}